1. Field of the Invention
This invention relates to dental drilling equipment, and in particular to pneumatic control assemblies therefore.
2. Prior Art
In conventional pneumatically operated and controlled dental drilling apparatus, as best exemplified by apparatus described in U.S. Pat. No. 3,638,310, each hand piece has a penumatically driven turbine for operating the drill bit and air and water nozzles through which air and water can, selectively, be directed for cooling and lubricating purposes. During a drilling operation, control of pressurized air to the turbine jet and water jet is effected by operation of a foot operated valve. Prior art equipment is so arranged that air which passes through the foot valve is directed as operating air to the hand piece turbine and, selectively, by manually operated selector switches, to either the air delivery jet in the hand piece or to an air pressure operated pilot valve regulating flow of water from a pressurized water source to the water jet in the hand piece.
This type of equipment has one major problem in that, due to the length of the air conduits required to extend from the air supply and thence through the foot valve and thence back to the manifold assembly to which each hand piece is connected, pressure drop due to friction is such that the air pressure is sufficient as operating pressure for the drill turbine but is insufficient as pilot pressure for operating the water pilot valve.